1. Field of the Invention
The present invention relates to an optical disk drive and, more particularly, to a laser controller for controlling a laser equipped in a pickup of the optical disk drive.
2. Description of the Related Art
A pickup for reading light reflected from a laser irradiated on an optical disk contains a laser driver for driving a laser. Recent technology advances to develop multi-intensity recording lasers, as well as a more high precision architecture for adjusting the pulse width of recording lasers. In order to bring about changes to multi-intensity recording lasers, as well as changes to a more high precision adjustment of the pulse width of recording lasers, the laser driver controls the irradiation timing as well as the output level of the recording laser. A “timing signal” is a signal that controls the timing for changing output levels of the laser. An electric current-setting signal is used to control the output level of the laser. The timing signal is normally transmitted to the laser driver as parallel data.
Optical disks devices are roughly classified with pickups, and the print circuit boards equipped with circuits such as controllers. A technique of mounting a timing controller generating the timing signal and a laser driver inside of the pickup has been proposed (hereinafter referred to as a “first background art”). A technique of mounting a laser driver inside of the pickup, and establishing a timing controller on the circuit board has also been proposed (hereinafter referred to as a “second background art”). Because the pickup is able to repeatedly shift back and forth within the inner and the outer confines, the pickup is connected to the print circuit board by means of a cable possessing flexibility, that is, a flexible-cable.
Concerning the first background art, by mounting the timing controller inside of the pickup, heat given off by the timing controller leads to an increase in the heat level inside of the pickup. It is difficult to mount a heat-diffusing structure in the limited space inside of the movable pickup. As a result, the properties of the laser device deteriorate due to the heat given off by the timing controller. Furthermore, the power requirements of the timing controller increase the overall power consumption level of the pickup. Things such as preset data used for subtle adjustments in the irradiation timing of the laser, as well as recording data modulated by a modulator become essential to the timing controller as input signals. Since things like the preset data and the recording data are transmitted to the timing controller via the flexible cable, the number of signal lines that the flexible cable possesses must increase. The more signal lines that the flexible cable possesses the heavier it becomes, which negatively affects the performance of the pickup.
Concerning the second background art, a delay occurs each time a timing signal passes through the flexible cable. When waveform distortion occurs in the laser's electric current by the delay difference of the timing signals transmitted as the parallel data, a fall in the precision of the irradiation timing of the laser results. The integrity of the data recorded on the optical disk will fall proportionately to the amount of drop in the precision of the irradiation timing of the laser. This becomes a large problem for optical disk devices that record at high speed. Consequently, additional circuitry such as resistors becomes needed as a countermeasure against signal delays. In recent years, due to increases in recording speed and increases in the density of recording media, timing control for switching the laser drive current has come to require resolution at a precision of several hundred [ps]. Therefore, there arises the need to increase the frequency of a resistor-employing exterior clock, which limits efforts at attaining high precision. Because of this limit on attaining high precision, it is impossible to sufficiently raise recording integrity in instances where a signal delay occurs.